JP2557710B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Industrial field of application) The present invention relates to an image forming apparatus using electrostatic transfer means such as an electrostatic copying machine and a printer.

(Problems to be Solved with Prior Art) An image of a laser beam printer or the like of the above-described image forming apparatus, which uses a transfer roller that performs image formation by reversal development using a laser beam and uses contact with an image carrier. In the forming device, at the time of pre-rotation at the beginning of operation,
To prevent toner from adhering to the transfer roller during non-sheet passing, such as during sheet passing during continuous sheet feeding, and by applying a bias of the opposite polarity to the charging polarity of the image carrier during non-sheet passing. In order to suppress the occurrence of transfer memory, it is usual to apply a voltage having the opposite polarity to that at the time of transfer (the same polarity as the toner) when the paper is not passed.

FIG. 5 is an outline of a sequence showing the state in this case. In order to prevent the residual toner on the surface of the image carrier from adhering to the transfer roller at the time of pre-rotation, the transfer roller is biased with the same polarity as the toner, for example, Apply −800V.

At the time of the next sheet passing, in order to perform a predetermined transfer, + 500V having a polarity opposite to that of the toner is applied.

Between sheets, as described above, −800V having the same polarity as that of the toner is applied.

Further, the charging bias is denoted by a symbol A on the leading end side of the transfer material so as to prevent the developing bias from being turned on at the uncharged portion of the image carrier and the portion being developed.
It is assumed that the trailing edge side is turned on for a longer time than the sheet passing time with a margin as indicated by a symbol B.

In such an image forming apparatus, the polarity of the bias voltage applied to the transfer roller is the same as that of the toner charged to the regular polarity during the pre-rotation and the sheet interval, and thus the polarity is opposite to that. Inverted toner that is present is inevitably absorbed by the transfer roller.

In particular, as shown in FIG. 5, since the charging area is wider than the developing area, the reversal toner is surely developed in that area, that is, the area indicated by reference numerals A and B. This adheres to the transfer roller and causes backside smearing of the transfer material.

The present invention has been made to cope with such a situation, and an object of the present invention is to provide an apparatus in which the back surface of a transfer material is not stained by a transfer rotating body.

(2) Configuration of the Invention (Technical Means for Solving the Problem and Its Action) In order to achieve the above object, the present invention provides an image carrier for carrying a toner image, and the toner image on the transfer material from the image carrier. A transfer rotator for transferring a transfer rotator which is in contact with a surface of the transfer material sent between the image carrier and the transfer rotator, the surface being opposite to the surface on the image carrier side; In an image forming apparatus having an electric field forming means for forming an electric field between the image carrier and the transfer rotary member, in one period when there is no transfer material between the image carrier and the transfer rotary member,
The electric field forming means transfers a toner having the same polarity as the charging polarity of the toner image from the transfer rotator to the image carrier, and a second electric field in a direction opposite to the first electric field. And (2) are formed on at least the entire circumference of the transfer rotating body, or in the above (1), the second electric field is formed after the first electric field is formed. An electric field is formed, and after the transfer rotator makes one or more rotations after the start of the second electric field formation, the transfer material reaches between the image carrier and the transfer rotator during the formation of the second electric field. In the image forming apparatus (2) or the above (1) or (2), when the first electric field is formed, the transfer rotary member has the same charge polarity as the toner image. An image forming apparatus characterized in that a voltage of polarity is applied. (3) Or in any one of (1) to (3) above, a voltage having a polarity opposite to the charging polarity of the toner image is applied to the transfer rotary member when the second electric field is formed. In the image forming apparatus (4) or any one of the above (1) to (4), when the first and second electric fields are formed, In the image forming apparatus (5) characterized in that a DC voltage is applied, or in any one of the above (1) to (5), the first and second electric fields are generated by the transfer rotating body. In the image forming apparatus (6), which is formed before the start of image transfer, or in any one of the above (1) to (6), the first and second electric fields are the transfer rotation. An image shape characterized by being formed after the image transfer by the body is completed In the device (7) or any one of the above (1) to (7), the first electric field is applied in one period in which there is no transfer material between the image carrier and the transfer rotator. In the image forming apparatus (8), or in any one of the above (1) to (8), characterized in that the period during which is formed is longer than the period during which the second electric field is formed. An image forming apparatus (9) characterized in that a voltage having a polarity opposite to the charging polarity of the toner image is applied to the transfer rotator at the time of image transfer by the transfer rotator, or in the above (1) to (9). In any one of the above, the image carrier is an electrophotographic photosensitive member, and the image forming apparatus (10) is provided.

With this configuration, it is possible to prevent toner from adhering to the transfer member, maintain good transfer, and reliably prevent backside smearing of the transfer material.

(Description of Embodiments) FIG. 1 is a schematic side view showing the configuration of a laser printer suitable for applying the present invention. An image carrier having an axis line in the direction perpendicular to the plane of the drawing and rotating in the direction of the arrow shown By the primary charger 2, the OPC photosensitive layer on the surface of (photoreceptor) 1
It is uniformly charged to −700 V, and the charged surface is irradiated with the image-modulated laser beam 3 to form an electrostatic latent image.

When the latent image arrives at the developing portion facing the developing device 4,
Negatively charged toner is supplied through the developing sleeve 4a and adheres to the latent image portion to form a toner image.

The developing sleeve 4a receives a peak-to-peak voltage from the power supply 4b.
A bias in which a DC voltage of -460V is superimposed on an AC voltage of 1200V and a frequency of 1800Hz is applied.

Next, when this toner image reaches the transfer portion where the transfer roller 6 which is the transfer rotary member is in pressure contact with the photosensitive member 1, the transfer material (not shown) is supplied to the transfer portion from the transport path 5 at the same timing. At the same time, a positive bias is applied to the transfer roller to transfer the toner image on the photoconductor to the transfer material.

After that, the transfer material carrying the toner image is conveyed to a fixing portion (not shown) via the conveying path 9, and the toner remaining on the photoconductor without being transferred to the transfer material at the transfer portion is retained by the cleaner 7 and on the photoconductor. The charges are eliminated by the pre-electrification lamp 8 and the photoconductor enters the next step.

The operation of such an image forming apparatus will be described below with reference to the timing charts shown in FIGS.

At the time point X, pre-rotation starts, and during this time, the toner adhering to the surface of the photoconductor 1 is not attracted to the transfer roller 6 due to, for example, a jam, so that the toner is adhering to the transfer roller 6 at the same time. In order to form the first electric field for transferring the negative toner to the photoconductor 1, a bias of the same polarity as the toner, in this case, -800 V is applied, and the time D is set longer than the time for the transfer roller 6 to make one rotation. I am doing it.

After time D has elapsed and before time C before starting the paper passing step, the bias polarity of the transfer roller 6 is changed to transfer the reverse toner contained in the normally charged toner to the photoconductor. Second
To form an electric field. This time C is set to be longer than one rotation of the transfer roller 6.

By doing so, the toner that moves to the photoconductor in the areas A and B described above is also not attracted to the transfer roller 6.

Since the amount of the normally charged toner is larger than that of the reversal toner, the time D is preferably longer than the time C as shown in FIG.

Although not shown in the drawing, it can be easily understood that the same operation can be achieved also by performing the same sequence as in the case of the above-described forward rotation during the backward rotation.

As described above, at the time of pre-rotation and post-rotation, the bias having the same polarity as that of the toner for the time longer than one rotation of the transfer roller between the sheets, and the bias having the polarity reversed for the time more than one rotation of the transfer roller. By applying, it is possible to remove not only the normally charged toner that has adhered to the transfer roller but also the reverse toner, so that good transfer can be performed stably over a long period of time, and the occurrence of back stain on the subsequent transfer material can be avoided. can do.

FIG. 3 is a timing chart showing another embodiment of the present invention.

In the illustrated system, the time point (corresponding to the time C in the above-described embodiment) at which a bias having the same polarity as that at the time of transfer is applied is
The feature is that it is not placed at the time of connecting when passing the paper.

That is, since the normally charged toner and the reversed toner can be removed by continuously applying the bias of positive and negative polarities only for the time exceeding the one rotation of the transfer roller, it is necessary to perform this between the sheets. The structure is shown in FIG.

In addition, the bias level in step C can be lowered to a level at which it becomes difficult to generate a memory on the photoconductor.

FIG. 4 shows still another embodiment of the present invention, in which only the photoconductor 1, the transfer roller 6 and its vicinity are shown.

If the diameter of the transfer roller is larger than the diameter of the photoconductor,
When the time between sheets is short, it may be difficult to apply positive and negative biases to the transfer roller to make one rotation each.

The illustrated apparatus is suitable for application in such a case.

This will be described with reference to this apparatus.
The electrode rollers 10a and 10b made of a conductive material such as grounded metal are in contact with the scrapers 11a and 11b attached to the toner containers 12a and 12b, respectively.

With this configuration, the toner removing portion that adheres to the transfer roller is removed at one point where the transfer roller contacts the photoconductor and at two points where the transfer roller contacts the electrode roller.
Since there are a total of three locations, if these points are arranged so as to divide the circumference of the transfer roller into three parts, the time corresponding to one rotation of the transfer roller will be 1/3 of the normal time.

Therefore, when the transfer roller has a large diameter as described above,
Cleaning of the transfer roller can be smoothly performed even when the paper interval is small.

The present invention has been described above with respect to the case where the photosensitive layer is made of an OPC photosensitive material and image formation is performed by reversal development, but the present invention is not limited to such a case, and other photosensitive materials and development methods can be used. It can be easily understood that the invention can also be applied to an image forming apparatus using.

Furthermore, in the above embodiments, the case where the transfer roller is used as the transfer means has been described, but the present invention is not limited to the roller type, and the present invention can be similarly applied to the transfer belt. By the way.

(3) Effects of the Invention As described above, according to the present invention, it is possible to effectively prevent both the normally charged toner and the reversal toner from adhering to the transfer rotary member, so that stable transfer is always performed. This can be carried out and the back stain of the transfer material can be prevented from occurring, which greatly contributes to obtaining a high quality image.

[Brief description of drawings]

FIG. 1 is a schematic side view of a main part of an image forming apparatus suitable for applying the present invention, FIG. 2 is a sequence diagram showing the operation of the same, FIG. 3 is a sequence diagram showing another embodiment, and FIG. FIG. 5 is a schematic side view of a main part of an image forming apparatus according to another embodiment of the present invention, and FIG. 5 is a sequence diagram of a known apparatus. 1 ... Photoconductor, 2 ... Primary charger, 3 ... Image signal, 4
…… Developing device, 5 …… Conveying path, 6 …… Transfer roller, 7 ……
Cleaner, 8 ... Front static elimination lamp, 10a, 10b ... Electrode roller, 11a, 11b ... Scraper.

Continuation of the front page (56) Reference JP-A-54-63838 (JP, A) JP-A-63-194283 (JP, A) JP-A-63-247781 (JP, A) JP-A-61-99179 (JP , A) JP 61-86775 (JP, A) JP 58-102278 (JP, A) JP 54-63837 (JP, A) JP 63-56674 (JP, A) JP 1-195459 (JP, A)

Claims (10)

(57) [Claims] 1. An image carrier for carrying a toner image, and a transfer rotator for transferring the toner image from the image carrier to a transfer material, the image carrier being provided between the image carrier and the transfer rotator. An image having a transfer rotator in contact with the surface of the transferred transfer material opposite to the surface on the image carrier side, and an electric field forming means for forming an electric field between the image carrier and the transfer rotator. In the forming apparatus, the electric field forming unit causes the toner having the same polarity as the charging polarity of the toner image to be transferred from the transfer rotator from the transfer rotator in one period in which there is no transfer material between the image carrier and the transfer rotator. An image formation, characterized in that a first electric field to be transferred to the image carrier and a second electric field in a direction opposite to the first electric field are formed on at least the entire circumference of the transfer rotator. apparatus. 2. The second electric field is formed after the formation of the first electric field, and the transfer rotary body is set to 1 after the formation of the second electric field is started.
The image forming apparatus according to claim 1, wherein the transfer material reaches between the image bearing member and the transfer rotating member during the formation of the second electric field after the rotation or more. 3. The image according to claim 1, wherein when the first electric field is formed, a voltage having the same polarity as the charging polarity of the toner image is applied to the transfer rotating body. Forming equipment. 4. The voltage according to claim 1, wherein a voltage having a polarity opposite to a charging polarity of the toner image is applied to the transfer rotary member when the second electric field is formed. Image forming device. 5. The image forming apparatus according to claim 1, wherein a DC voltage is applied to the transfer rotary member when the first and second electric fields are formed. 6. The image forming apparatus according to claim 1, wherein the first and second electric fields are formed before the start of image transfer by the transfer rotating body. 7. The image forming apparatus according to claim 1, wherein the first and second electric fields are formed after image transfer by the transfer rotating body is completed. 8. A period in which there is no transfer material between the image carrier and the transfer rotator, and a period in which the first electric field is formed is longer than a period in which the second electric field is formed. 8. The image forming apparatus according to claim 1, wherein the image forming apparatus is also long. 9. The image according to claim 1, wherein a voltage having a polarity opposite to the charging polarity of the toner image is applied to the transfer rotary member when the image is transferred by the transfer rotary member. Forming equipment. 10. The image forming apparatus according to claim 1, wherein the image bearing member is an electrophotographic photosensitive member.